the innovative Soviet technologies. 1937 Fire-fighting sport Fire-fighting sport is a sport discipline that includes a competition between various fire fighting teams in fire fighting-related exercises, such as climbing special stairs in a mock-up house, unfolding a water hose, and extinguishing a fire using hoses or extinguishers. It was developed in the Soviet Union in 1937, while international competitions have taken place since 1968. 1937-1957 ANS synthesizer 1938 Deep column station The deep column station is a type of subway station, consisting of a central hall with two side halls, connected by ring-like passages between a row of columns. Depending on the type of station, the rings transmit load to the columns either by "wedged arches" or through purlins, forming a "column-purlin complex." The fundamental advantage of the column station is the significantly greater connection between the halls, compared with a pylon station. The first deep column station in the world is Mayakovskaya, designed by Alexey Dushkin and opened in 1938 in Moscow Metro. 1938 Sambo Sambo (an acronym, Самбо stands for САМооборона-Без-Оружия, meaning "self-defence without weapons") is modern martial art, combat sport and self-defense system developed in the Soviet Union and recognized as an official sport by the USSR All-Union Sports Committee in 1938, presented by Anatoly Kharlampiev. 1939 Kirlian photography By Semyon Kirlian 1939 Vought-Sikorsky VS-300 The world's first tail rotor helicopter and first amphibious helicopter by Igor Sikorsky. 1939 Ilyushin Il-2 The world's most produced combat aircraft. 1939 Self-propelled multiple rocket launcher Katyusha rocket launcher 1940s 1940s Ballast cleaner 1940s TRIZ 1940s Sikorsky R-4 The R-4 was the world's first mass-produced helicopter and the first helicopter used by the United States Army Air Forces, Navy, Coast Guard, and the United Kingdom's Royal Air Force and Royal Navy. 1940 T-34 tank by Mikhail Koshkin, the most produced tank of World War II 1941 Competitive rhythmic gymnastics 1941 Maksutov telescope by Dmitri Dmitrievich Maksutov 1941 Degaussing by Anatoly Petrovich Alexandrov, independently from Charles F. Goodeve 1942 Winged tank Antonov A-40 by Oleg Antonov 1942 Gramicidin S by Georgy Gause 1944 Microtron 1944 EPR spectroscopy by Yevgeny Zavoisky 1945 T-54/55 tank World's most produced tank. 1945 Passive resonant cavity bug by Léon Theremin 1946 Heart-lung transplant by Vladimir Demikhov 1947 Modern multistage rocket by Mikhail Tikhonravov and Dmitry Okhotsimsky 1947 MiG-15 World's most produced jet aircraft. 1947 AK-47 The AK-47 (other names include Avtomat Kalashnikova, Kalashnikov, or AK) is a